無法獲取列表中已安裝的應用程序列表<String>

Question

下面是我將所有已安裝的應用程序的名稱放入List中的功能 。

功能下面是失敗的堆棧跟蹤 - 我做錯了什么？

@SuppressWarnings("null")
private List<String> getInstalledAppsList() {
    List<String> l_installedApps = null;

    List<PackageInfo> allPackagesList = getPackageManager().getInstalledPackages(PackageManager.GET_META_DATA);

    PackageManager pm = getPackageManager();

    for(int i = 0 ; i < allPackagesList.size() ; i++) {
        PackageInfo p = allPackagesList.get(i);

        l_installedApps.add(p.applicationInfo.loadLabel(pm).toString());  //THIS IS WHERE EXCEPTION IS OCCURRING
    }

    return l_installedApps; 
}

失敗的Stacktrace ：

05-26 21:59:22.128: E/AndroidRuntime(3270): FATAL EXCEPTION: main
05-26 21:59:22.128: E/AndroidRuntime(3270): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mavdev.focusoutfacebook/com.mavdev.focusoutfacebook.MainActivityCircularSeekbar}: java.lang.NullPointerException
05-26 21:59:22.128: E/AndroidRuntime(3270):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at android.os.Looper.loop(Looper.java:137)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at android.app.ActivityThread.main(ActivityThread.java:5103)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at java.lang.reflect.Method.invokeNative(Native Method)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at java.lang.reflect.Method.invoke(Method.java:525)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at dalvik.system.NativeStart.main(Native Method)
05-26 21:59:22.128: E/AndroidRuntime(3270): Caused by: java.lang.NullPointerException
05-26 21:59:22.128: E/AndroidRuntime(3270):     at com.mavdev.focusoutfacebook.MainActivityCircularSeekbar.getInstalledAppsList(MainActivityCircularSeekbar.java:2045)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at com.mavdev.focusoutfacebook.MainActivityCircularSeekbar.onCreate(MainActivityCircularSeekbar.java:798)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at  android.app.Activity.performCreate(Activity.java:5133)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-26 21:59:22.128: E/AndroidRuntime(3270):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
05-26 21:59:22.128: E/AndroidRuntime(3270):     ... 11 more

Answer 1

l_installedApps = null

你在哪里初始化它？

在添加項目之前你應該這樣做：

l_installedApps = new ArrayList<String>();

Answer 2

這就是拋出NullPointerException，因為l_installedApps為null。 你應該像這樣初始化它：

List<String> l_installedApps = new ArrayList<String>();

一定要導入

java.util.ArrayList;